1. Field of the Invention
The present invention relates to a stereoscopic display device and a driving method thereof, and more particularly, to a stereoscopic display device having a parallax barrier liquid crystal display panel and a driving method thereof.
2. Discussion of the Related Art
Until now, a two-dimensional display device is generally used. Recently, according to the high-speed of information by using a communication network with a wideband, a three-dimensional display device has been researched and developed.
In general, the three-dimensional display device displays stereoscopic images using a principle of a stereo vision through both eyes. In other words, a parallax of both eyes acts as a primary factor to display three-dimensional images. When the right and left eyes look at respective two two-dimensional images, the two two-dimensional images are transferred to the brain and then the brain mixes the two two-dimensional images. Thus, the three-dimensional images having the depth and reality are played back.
Based upon the above principle, as three-dimensional display devices displaying three-dimensional images by using two-dimensional images, a stereoscopic display device with a specific glasses, a stereoscopic display device without glasses, a holographic display device and so on have been used. The stereoscopic display device with a specific glasses has disadvantages such as inconvenience and unnaturalness due to wearing the separate specific glasses. The holographic display device has a technical difficulty due to using a laser reference beam and has a requirement for a large space due to the large size of the equipment. However, the stereoscopic display device without glasses does not require a separate specific glasses and its equipment is simple. The stereoscopic display devices without glasses are divided into a parallax barrier type, a lenticular type and an integral photography type. Of these types, presently, the parallax barrier type has been mainly used.
FIG. 1 is a cross-sectional view illustrating a parallax barrier type stereoscopic display device according to the related art.
As shown in FIG. 1, the parallax barrier type stereoscopic display device includes a liquid crystal display panel 10, a backlight 20 below the liquid crystal display panel 10, and a parallax barrier 30 between the liquid crystal display panel 10 and an observer 40. A left eye pixel L and a right eye pixel R are alternatingly formed in the liquid crystal display panel 10. A slit 32 and a barrier 34 are alternatingly formed in the parallax barrier 30. Each of the slits 32 and the barriers 34 has a stripe pattern. Of lights emitted from the backlight 20, a first light L1 passing through the left eye pixel L goes to the observer's left eye through the slit 32, while the second light R1 passing through the right eye pixel R goes to the observer's right eye through the slit 32. Images displayed through the left and right eye pixels L and R have parallax information which human can sufficiently perceive. Thus, the observer 40 perceives three-dimensional images.
However, since the slits and barriers are fixed, the parallax barrier type display device is used only for displaying three-dimensional images. To solve this limitation, the stereoscopic display device converting between a two-dimension mode and a three-dimension mode has been used.
FIGS. 2A and 2B are cross-sectional views illustrating a two-dimension mode and a three-dimension mode, respectively, of a stereoscopic display device having a parallax barrier liquid crystal panel according to the related art.
As shown in FIGS. 2A and 2B, the stereoscopic display device includes a backlight 50, a main liquid crystal panel 60, and a parallax barrier liquid crystal panel 70 between the backlight 50 and the main liquid crystal panel 60. The main liquid crystal panel 60 includes first and second substrates 64 and 66, and a first liquid crystal layer 62 between the first and second substrates 64 and 66. Though not shown in the drawings, a plurality of pixel electrodes and thin film transistors (TFTs) are disposed in a matrix form on the first substrate 64, and a plurality of color filter patterns, a black matrix and a first common electrode are disposed below the second substrate 66.
The parallax barrier liquid crystal panel 70 includes third and fourth substrates 74 and 78, and a second liquid crystal layer 72 between the third and fourth substrates 74 and 78. A barrier electrode 76 having a stripe pattern is disposed on the third substrate 74 and a second common electrode 80 is disposed below the fourth substrate 78. The barrier electrode 76 and the common electrode 80 are transparent. First, second and third polarizing plates 82, 84 and 86 are formed respectively on the second substrate 66, between the main liquid crystal panel 60 and the parallax barrier liquid crystal panel 70, and below the third substrate 74.
Suppose that the parallax barrier liquid crystal panel 70 is driven by a Normally White (NW) mode, the parallax barrier liquid crystal panel 70 has a white state in a two-dimensional mode.
As shown in FIG. 2A, in a two-dimension mode, no driving voltage is applied to the barrier electrode 76, and thus the parallax barrier liquid crystal panel 70 has a normally white state entirely. Accordingly, the light emitted from the backlight 50 is transmitted through the parallax barrier liquid crystal panel 70. As a result, an observer can see plane images (i.e., two-dimensional images) of the main liquid crystal panel 60. On the contrary, as shown in FIG. 2B, in a three-dimension mode, a driving voltage is applied to the barrier electrode 76, and thus the second liquid crystal layer 72 between the barrier electrode 76 and the second common electrode 80 is driven. Accordingly, a zone of the parallax barrier liquid crystal panel corresponding to the barrier electrode 76 shields the light emitted from the backlight 50, which is referred to as a barrier-zone BZ having a black state. On the contrary, a zone between the barrier zones BZ transmits the light emitted from the backlight 50, and thus it is referred to as a transmission zone TZ having a white state. The barrier-zone B and the transmission-zone T respectively act as a barrier and a slit, as shown in FIG. 1. Accordingly, an observer can perceive two-dimensional images (plane images) of the main liquid crystal display panel 60 as three-dimensional images (stereo images). As a result, a dimension mode of the stereoscopic display device can be selectively converted between a two-dimension mode and a three-dimension mode in accordance with the on/off states of the barrier electrode 76.
FIG. 3 is a cross-sectional view illustrating another stereoscopic display device having a parallax barrier liquid crystal panel according to the related art. Detailed explanations of parts similar to parts of FIGS. 2A and 2B will be omitted.
As shown in FIG. 3, a stereoscopic display device includes a main liquid crystal panel 60, a backlight 50 and a parallax barrier liquid crystal panel 70 similarly to the stereoscopic display device of FIGS. 2A and 2B. However, the parallax barrier liquid crystal panel 70 has structures different from the structures of the parallax barrier liquid crystal panel of FIGS. 2A and 2B. In other words, in a transmission-zone TZ, a partition wall 90 of transparent photo acryl is formed instead of a liquid crystal layer 72, and in a barrier-zone BZ, the liquid crystal layer 72 is formed. Accordingly, a boundary between the transmission-zone TZ and the barrier-zone BZ is distinctly divided, and the stereoscopic display device selectively displays a two-dimensional image and a three-dimensional image.
As explained above, the related art stereoscopic display devices having the parallax barrier liquid crystal panel have advantages, such as a selective conversion between a two-dimension mode and a three-dimension mode. However, the related art stereoscopic display devices have disadvantages, such as a low brightness and a low sensory resolution in a three-dimension mode. In other words, as a width of the transmission-zone TZ decreases, a sensory resolution increases. However, as a width of the transmission-zone TZ decreases, an aperture ratio also decreases and thus a brightness decreases. FIG. 4 is a conceptual plan view illustrating a screen in a three-dimension mode of the related art stereoscopic display device having a parallax barrier liquid crystal panel. As shown in FIG. 4, an area of a transmission-zone TZ is very small. Accordingly, if the area of the transmission-zone T becomes smaller, the aperture ratio and the brightness decrease rapidly. Characters R, G and B represent red, green and blue pixels of the main liquid crystal panel. As a result, the related art stereoscopic display device has limits to displaying three-dimensional images because the sensory resolution decreases for maintaining the brightness to some degree.